Ghost of SARS haunts Toronto in LTC outbreak

Ghost of SARS haunts Toronto in LTC outbreak

Legionnaires’ disease kills 17 at nursing home

Initially sensationalized as a mystery bug, the pathogen that caused a recent outbreak that claimed 17 lives in an Toronto nursing home turned out to be one of the usual suspects: Legionella pneumophila.

However, a city that was beset by the global outbreak of severe acute respiratory syndrome (SARS) in 2003 revisited some of the public hysteria in the first few days of an outbreak that began on Sept. 25, 2005. As more cases of pneumonia of an unknown etiology rapidly appeared, hospitals treated the cases under infection control precautions suitable for SARS or another communicable respiratory pathogen.

Legionnaires’ disease, of course, does not spread from person to person, but protecting health care workers was foremost in the mind of the responding hospitals. As a result, full respiratory isolation precautions were implemented as laboratorians furiously tried to identify the pathogen over the course of several days.

"Post-SARS, our responsibility to our health care workers is to be as careful as possible," says Allison McGeer, MD, FRCPC, director of infection control at Mount Sinai Hospital in Toronto. "So we recommended additional precautions. I think what probably happened was that the response triggered some discussion among the emergency medical services on lines that are accessible to the media should they choose to listen. That triggered a media panic. It started on a Friday night and was full blown by the time public health had a chance to respond with a press conference on Saturday."

Then — again echoing the SARS epidemic — after the local media was sufficiently reassured, international publicity spurred a second wave of speculation and hysteria. "The Toronto media were actually pretty good," McGeer says. "It took them a couple of days to calm down, but they listened to what the public health unit was saying. It was the same as SARS, when people in Toronto knew about it and nobody was that worried about it anymore, suddenly the international media decided it was a story."

Each year, 8,000 to 18,000 cases of Legionnaires’ disease occur in the United States, with some 10% to 20% of cases as part of outbreaks.¹ Case-fatality rates in outbreaks typically are 20% to 40%.

The outbreak at Seven Oaks Home for the Aged in Toronto falls into that range, with 17 deaths out of 70 cases. In addition, 45 residents were hospitalized. The disease is caused by Legionella bacteria, which can proliferate in pipes and tanks of water systems. Transmission occurs through inhalation of an aerosol containing the bacteria or by aspiration of contaminated water. Many outbreaks have been traced to drinking water and cooling towers. The source of the Toronto outbreak remains under investigation. The potable water supply, ventilation system, shower heads, and ice machines in the facility are all being cultured. Results were not available as this issue went to press.

"This doesn’t look like an outbreak associated with contamination of the potable water supply," McGeer says. "It looks a lot like a point source outbreak."

Such outbreaks have been traced to fountains, hot tubs and water displays, but the nursing home has none of the above.

"There is no mistable water anywhere in the facility at any time that any of us have been able to identify," she says. "That leaves an external source. This building is relatively isolated. There are a limited number of water towers it could come from, and we are still waiting from cultures for those. [We are also trying to determine] the status of those and whether anybody did anything to them that might have caused this."

A construction site is in the area, but Legionella carried by dispersed soil is not thought to be the likely cause. "An outbreak of this size has certainly never been described from a soil source before," she says.

Eight of the 17 deaths have been autopsied, and Legionella was confirmed in three cases. There are other lab reports of Legionella in lung tissue, but a slim possibility remains that at least some of the infections were caused by another respiratory agent. "The Legionella may be a coinfection," McGeer says. "Only time will tell, but I think that’s unlikely. Heaven knows, we investigated the heck out of this outbreak in the lab. We have not been able to find a virus."

Indeed, one positive outcome of the outbreak could be more resources for improved lab testing, she notes. While it actually was not an issue in outbreak management, the storm of public concern could have been tamped down much quicker with a more rapid diagnosis.

"For us in Ontario, I think it will be an encouragement to continue the rebuilding of our public health lab [capacity] and, for all sorts of reasons, that is very important," she says.

Reference

1. Kool JL, Carpenter J, Fields BS. Effect of monochloramine disinfection of municipal drinking water on risk of nosocomial Legionnaires’ disease. Lancet 1999; 353:272-277.